The present invention relates to a centralizer for use in wellbore operations. More specifically, the present invention relates to a centralizer with movable bow springs, particularly a stabilizer that is used in relatively small annular spaces and which also expands for use in a larger annular space. In another aspect, the present invention relates to a centralizer that provides a minimum standoff and/or centralization in portions of a wellbore in which known bow spring centralizers cannot provide adequate standoff because the bow springs lack sufficient restoring force.
Bow spring centralizers are used to center one tubular member inside a borehole or other tubular member, e.g., to center a first smaller casing in a second larger casing. Typically, centralizers are run into the borehole on the exterior of an inner tubular member or pipe string and project radially outwardly from the outside diameter (O.D.), or surface of the smaller tubular member into contact with the inside diameter (I.D.), or surface of the larger diameter tubular. However, a disadvantage of such centralizers is that they restrict fluid flow in the annular space.
Many wells include a portion that is cased and a portion that is not cased. In other wells, the diameter of the bore changes, or the well includes one or more lateral bores. Downhole operations are conducted in cased, uncased, different diameter, and/or lateral bores. In such wellbores, the centralizer must pass through a portion of the bore that is relatively small and then down through a portion that is smaller, with the centralizing function needed in the larger diameter, deeper portion of the wellbore. So far as is known, no centralizer is available that can be run into such bores and then provide effective centralizing in a larger diameter portion of the wellbore. Similarly, no centralizer is known that provides effective centralizing in bores of both diameters.
Another limitation of known centralizers occurs in the curved portion of a wellbore. In such wellbores, the weight of the tilting or pipe to which the centralizer is mounted exceeds the restoring force of the bow springs such that the tubing or pipe bears against the side of the wellbore.
There is, therefore, a need for, and it is an object of the present invention to provide, a centralizer that positions the tubing or pipe string off the side of the wellbore in the curved portion of the wellbore.
It is also an object of the present invention to provide positive centralization in areas of the wellbore where a bow spring is not strong enough to position the pipe or tubing string off the side of the well bore but also provide standoff in less severe portions of the borehole.
Another object of the present invention is to provide a centralizer that functions in both a large and/or small diameter annulus and/or wellbore.
Another object of the present invention is to provide a centralizer that maintains both standoff from the wall of the borehole and fluid flow through the borehole.
Yet another object of the present invention is to provide a centralizer that can be run into a borehole through a borehole of small diameter, e.g., a cased portion of the borehole, that also functions to center the tubing in a portion of the borehole having a diameter larger than the small diameter portion such as an uncased portion of the borehole.
Other objects, and the advantages, of the present invention will be made clear to those skilled in the art by the following description of a presently preferred embodiment thereof.
These objects are achieved by providing a centralizer comprising a body, a plurality of radially outwardly extending vanes on the body, and a collar mounted on the body. A plurality of bow springs are mounted to the collar, the bow springs being maintained in spaced relation to the vanes whereby one or more of the bow springs moves between a first, bowed position standing off from the body to a second compressed position between the vanes and closer to the body. When the bow springs are compressed into the spaces between vanes, the vanes, which are not compressible under normal operating conditions, provide standoff from the wall of the hole and maintain fluid flow past the centralizer. In a particularly preferred embodiment, the vanes extend radially outwardly from the surface of the body of the centralizer far enough that the effective diameter of the body at the location of the vanes is larger than the diameter of the body, thereby providing the standoff from the wall of the borehole.